Comment by PhasmaFelis

It sounds like microelectromechanical devices (like the quartz oscillators that keep time in electronics) are so small, and built to such fine tolerances, that helium atoms can literally, physically jam them like sand in a gearbox. That's what the article seems to be saying, anyway.

I guess they're fine under normal conditions because typical atmospheric molecules are actually too big to get inside? I'm not clear why the particular clock that Apple used is susceptible but other ones aren't. I guess they're sealed better.